Ionization of gaseous molecules is conventionally initiated by photon bombardment, charged particle impact, ultraviolet radioactive ionization, or by thermal electron beams. Such ionization techniques are typically utilized for mass spectrometers and ion mobility spectrometers. During ionization, depending on the level of impact energy, one of two events occur, either electrons are ejected from atoms and molecules or the molecules themselves are fractured into complement of fragments with diverse charge states. These processes are known as hard ionization and while they can be utilized to provide a measurement indicative of the atoms and molecules contained within the ionized sample, many components cannot be measured. Further, these xe2x80x98hardxe2x80x99 ionization mechanisms are inefficient with approximately 0.1% of atoms or molecules ionized. In addition, conventional mass spectrometers require low pressure (xe2x80x9chard vacuumxe2x80x9d) to operate to prevent higher velocity ions from colliding with a slower moving atoms and molecules (thermal velocities) that, during passage through the spectrometer, attenuate ion currents below detectable limits.
Moreover, conventional systems for ionization are susceptible to avalanche arcing when gases ionize in high electric fields. This phenomenon results because the mean free path length between molecules (at the relevant gas pressure) is greater than the electrode separation within the ionization device (empirical measurements showing the breakdown voltage versus gas pressure are identified in the Paschen curve of FIG. 1). If conventional systems could be configured to operate under the Paschen curve, then ionization would occur without avalanche arcing.
Current ionization systems coupled to detection systems are unable to characterize a wide range of biological matter. This is due in part because most biological matter comprises complex molecular structures that are susceptible to fracture, thus making it hard to characterize. In addition, some biological matter such as bacteria have varying masses depending on the stage of replication. Accordingly, as conventional techniques necessarily fracture the biological matter, users are forced to examine a spectrum of mass data corresponding to the various atoms and molecules that made up the examined matter rather than the overall mass of the biological matter.
In addition, there are many applications that utilize an ion or electron source that would benefit from a low cost efficient replacement such as field emission cathodes coated with low effective work-function materials. However, such cathodes are difficult and costly to manufacture and often have wide range of emissions and so there remains a need for an improved electron source.
It will be appreciated that there are other applications that are desirable for ionization including the characterization of ions by their valiancy, if an ionization system were sufficiently xe2x80x9csoftxe2x80x9d, efficient, small and inexpensive, and it is to this end that other aspects of the invention are directed.
The invention is disclosed in a robust, efficient, temperature-insensitive, compact, and easy to manufacture ionizing device with a substrate having at least one opening. The substrate includes a first conductive electrode on a first surface and a second conductive electrode extending on a second surface that are separated by an insulating element to form an opening between the electrodes the width of the insulator. Preferably, the thickness of the insulating element is less than 1 micron. In some embodiments, the ionizing device is coupled to a detection system to characterize genetic material such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and proteins for use in fields such as proteomics, drug discovery, diagnostics, identification of genetic material, metabolomics, and forensics. In addition, the detector elements within the detection system may be configured to collect detected genetic material so that they may later be blotted onto nitrocellulose paper.
In another embodiment, a system for producing ions and electrons is disclosed. This system includes an ionizing membrane having a thick supporting portion with pores formed therein. Like the ionizing device, the membrane has first and second metal electrodes coated on surfaces of the thick supporting portion extending into the pores. The distance between the first and second metal electrodes within the pores of the thick supporting portion is less than the mean free path of a molecule being ionized so that molecules ionized by the pore will be subject to secondary collision and thus fracture. A field generating element is also used for directing the ions and electrons produced by the ionizing membrane. The ions created by the system may be utilized for any application requiring a source of ions such as ion focused milling, maskless ion implantation, ion beam lithography, semiconductor mask modification, semiconductor chip wiring modifications, and ion mass spectrometry, as well as the supply of pure species for chemical reactors and biological reactors. Furthermore, as ions are produced, electrons are also xe2x80x9cstrippedxe2x80x9d from the molecules which are directed by the field generating element for use with applications such as discharge light sources, flat panel displays, thyratrons, microwave switches, diodes, triodes, tetrodes, pentodes, and other replacements for hot-cathodes.
In another embodiment, a valence spectrometer is disclosed that is configured to incrementally increase an ionization field so that all molecules with a valence level equal or below the ionization field strength will be ionized. Like the embodiments above, the system incorporates an ionizing device as described above that is configured to ionize molecules passing therethrough below a specific valence level. A detection element coupled to said ionizing device determines the number of ionized molecules.
Also disclosed is a system for ionizing multiple samples in parallel comprising an ionization membrane as described above with an array of pores. Coupled to the ionization membrane are a plurality of inlets configured to supply each sample to a single pore on the ionizing membrane. In addition, each pore may have one or more detector elements aligned thereto and configured to detect the passage of ions through the pores to a specified location (thereby providing measurements analogous to an ion mobility spectrometer). The current detected on the detector elements is proportional to the concentration of matter on such elements and can be used for quantitation measurements.
As many difficulties arise when ionizing a sample of biological matter, a technique is disclosed (which may be used alone or in combination with an ion characterization system) for ultrasonically resonating a sample to remove materials that either confuse or are not instructive for characterizing the constituents of the biological matter. The technique utilizes a system includes a tubular member configured to receive liquid samples having biological matter suspended therein. A piezoelectric generator is circumferentially coupled to the tubular member so that it may ultrasonically resonate the contents of the tubular member to remove undesirable matter. The resulting liquid is delivered to a vaporizer that vaporizes the liquid prior to ionization.
Also disclosed are a soft ionization device and ion characterization system for the characterization of nuclear, biological and chemical threats as well as a technique for generating a unipolar plasma.